Christmas light bulb plays a significant role in the decoration lighting market. However, the conventional Christmas light bulbs have some problems. For example, it is haunted by the problem of safety caused by its physical arrangement, lack of the ability of saving electrical power and hard to manipulate the exhibiting color. For the bulbs connected in series and used in decoration situation, the whole series of bulbs will be extinguished if only one of those lamps has problem. This problem will be more serious for those decorating lighting bulbs used in outdoor decoration, for those bulbs in such situation are liable to be deteriorated by a bad weather.
To overcome above problems, the present invention provides an optical fiber which has a plurality of micro-windows alone its outer surface, the light guided along the optical fiber can come out from those micro-windows in radial direction as it travels to those micro-windows to provide a uniform illumination in spot-like manner.
An optical fiber generally consists of a cylinder core of silica glass or plastic materials surrounded by a cladding whose refractive index is lower than that of the core and can be used in the field of data transmission, guided wave device, optical fiber sensor and decoration application. For a step-index plastic optical fiber, its has a core made of PMMA Polymethyl methacrylate and a cladding made of fluorinated polymer, and has excellent extension property and flexibility.
Referring to FIG. 1, this figure shows a step-index optical fiber and is used to explain the principle of guiding light wave for an optical fiber. The incident light is launched into the core of the optical fiber which is a homogeneous and has a larger refractive index, and the core is surrounded by a cladding which has a lower refractive index. By the principle of total internal reflection, the light launched into the core within a small angle will be reflected on the interface of the core and the cladding. That is, the light will be bounced forth and back within the core, in other word, be guided within the core. For a step-index plastic optical fiber, it has a thick core and a thin cladding. For example, in an optical fiber of 750 .mu.m diameter, the core has diameter of 735.+-.45 .mu.m, and the cladding with the core has total thickness of 750.+-.45 .mu.m.
Above discussion shows that the guidance of light wave in an optical fiber is realized by the total internal reflection occurred on the interface of the core and the cladding, which have different values of refractive index. By the principle of ray optics, the light wave will be guided losslessly alone the core if the light wave is launched into the core within a small angle. That is, the angle is such small that the condition of total internal reflection can be realized. However, there exists propagation loss in the optical fiber due to the imperfection in the materials and the structure of the optical fiber.
As to the mechanism accounting for the propagation loss of the optical fiber, there are the inherent absorption loss for the fiber materials. Taking fiber with an absorption loss of 0.2 dB/km as an example, the optical fiber will lose 7% of its light energy after a 2 meter propagation. Besides the inherent absorption loss in optical fiber, there are also the scattering loss due to the impurity and bulb generated during the pulling process of the optical fiber, the loss caused by the imperfection in the shape of the core . . . etc. FIG. 2 shows the relationship between the guided wave energy and the propagation distance for optical fibers to explain the effect of the propagation loss.
Because the light wave is not guided perfectly in real situation, there exists light wave scattered from the surface of the optical fiber. The scattered light can be employed for decoration purpose. However, for the optical fiber having above propagation loss mechanism can only illuminate weak or diversified light alone its surface and provide spot light only at its end, so it does meet the requirement of decoration satisfactorily. For a high propagation loss fiber, there might be more light wave emitting out of fiber in radial direction, however, the illumination is not uniform.
To solve the above problem, the present invention provide a fiber having continuous and uniform spot-like illumination, which can be advantageously employed in the field of decoration lighting.
The present invention provides a fiber having a radial illumination effect along a effective propagation distance, said fiber has a plurality of micro-windows cut in its outer surface, light can be illuminated from the micro-window as long as there is light launched into the fiber within the acceptance angle thereof.
More particularly, this invention use automatically-controlled and high-precision cutting means to machine the optical fiber, which cuts away a plurality of tiny region of the cladding and exposes those part of the core t under the opening. Therefore, the light wave guided within the core can illuminate uniformly from those opening if they incident to the opening.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention: